6,477 research outputs found
Exploring the Way to Approach the Efficiency Limit of Perovskite Solar Cells by Drift-Diffusion Model
Drift-diffusion model is an indispensable modeling tool to understand the
carrier dynamics (transport, recombination, and collection) and simulate
practical-efficiency of solar cells (SCs) through taking into account various
carrier recombination losses existing in multilayered device structures.
Exploring the way to predict and approach the SC efficiency limit by using the
drift-diffusion model will enable us to gain more physical insights and design
guidelines for emerging photovoltaics, particularly perovskite solar cells. Our
work finds out that two procedures are the prerequisites for predicting and
approaching the SC efficiency limit. Firstly, the intrinsic radiative
recombination needs to be corrected after adopting optical designs which will
significantly affect the open-circuit voltage at its Shockley-Queisser limit.
Through considering a detailed balance between emission and absorption of
semiconductor materials at the thermal equilibrium, and the Boltzmann
statistics at the non-equilibrium, we offer a different approach to derive the
accurate expression of intrinsic radiative recombination with the optical
corrections for semiconductor materials. The new expression captures light
trapping of the absorbed photons and angular restriction of the emitted photons
simultaneously, which are ignored in the traditional Roosbroeck-Shockley
expression. Secondly, the contact characteristics of the electrodes need to be
carefully engineered to eliminate the charge accumulation and surface
recombination at the electrodes. The selective contact or blocking layer
incorporated nonselective contact that inhibits the surface recombination at
the electrode is another important prerequisite. With the two procedures, the
accurate prediction of efficiency limit and precise evaluation of efficiency
degradation for perovskite solar cells are attainable by the drift-diffusion
model.Comment: 32 pages, 11 figure
Hyperbolic metamaterial as a tunable near-field spatial filter for the implementation of the active plasmon injection loss compensation scheme
We present how to physically realize the auxiliary source described in the
recently introduced active plasmon injection loss compensation scheme for
enhanced near-field superlensing. Particularly, we show that the
characteristics of the auxiliary source described in the active plasmon
injection scheme including tunable narrow-band and selective amplification via
convolution can be realized by using a hyperbolic metamaterial functioning as a
near-field spatial filter. Besides loss compensation, the proposed near-field
spatial filter can be useful for real-time high resolution edge detection.Comment: 8 pages, 8 figure
Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers
We demonstrate theoretically a strong local enhancement of the intensity of
the in-plane microwave magnetic field in multilayered structures made from a
magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two
non-magnetic layers with a high dielectric constant matching that of YIG. The
enhancement is predicted for the excitation regime when the microwave magnetic
field is induced inside the multilayer by the transducer of a stripline
Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous
numerical solution of the Landau-Lifshitz-Gilbert equation consistently with
the Maxwell's equations, we investigate the magnetisation dynamics in the
multilayer. We reveal a strong photon-magnon coupling, which manifests itself
as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by
the YIG layer and the electromagnetic resonance mode supported by the whole
multilayered structure. The frequency of the magnon mode depends on the
external static magnetic field, which in our case is applied tangentially to
the multilayer in the direction perpendicular to the microwave magnetic field
induced by the stripline of the BFMR setup. The frequency of the
electromagnetic mode is independent of the static magnetic field. Consequently,
the predicted photon-magnon coupling is sensitive to the applied magnetic field
and thus can be used in magnetically tuneable metamaterials based on
simultaneously negative permittivity and permeability achievable thanks to the
YIG layer. We also suggest that the predicted photon-magnon coupling may find
applications in microwave quantum information systems
Simulation of scattering from layered spheres with known surface electric field distributions using Mie theory and modified angular spectrum method: Applications to corneal sensing
Mie theory is a powerful method to evaluate the scattered fields from the
multilayered sphere, where the incident field is expanded to the vector
spherical harmonic (VSH) presentation. Then scattered fields are obtained by
the T-matrix method. However, obtaining the VSH coefficients for arbitrarily
shaped incident fields is difficult and time-consuming. This paper proposes a
novel 3D angular spectrum method (3D ASM) for evaluating the VSH coefficients
for the incident field, which is defined from the required electric field
distribution positioned on the spherical surface. This allows the VSH expansion
and evaluation of the scattered fields from a multilayered sphere illuminated
with an arbitrary incident wavefront in the Mie Scattering range. This has been
computationally challenging with previous methods.
First, the advantage of the beam created with the proposed method compared to
the nominal Gaussian beam illumination is addressed with the spherical bandstop
filter simulation. Then the incident field computed by the proposed method is
compared to the physical-optics simulations showing precise agreement. As an
example of the proposed methodology, the cornea is modeled as a multilayered
spherical structure, and the scattered fields are computed from the cornea
illuminated by the incident field with spherical top-hat and tapered top-hat
wavefronts. Also, the coupling coefficients of the incident and scattered
fields from the cornea model are computed in the 200 - 400 GHz frequency range.
The results are compared with coupling coefficients obtained with Gaussian beam
illumination and referenced to the reflectivity obtained from plane wave
illumination on an analog planar structure. The top-hat beams show increased
agreement with the planar stratified medium theory compared to the plane wave
and Gaussian beam illumination
Phase retrieval of reflection and transmission coefficients from Kramers-Kronig relations
Analytic and passivity properties of reflection and transmission coefficients
of thin-film multilayered stacks are investigated. Using a rigorous formalism
based on the inverse Helmholtz operator, properties associated to causality
principle and passivity are established when both temporal frequency and
spatial wavevector are continued in the complex plane. This result extends the
range of situations where the Kramers-Kronig relations can be used to deduce
the phase from the intensity. In particular, it is rigorously shown that
Kramers-Kronig relations for reflection and transmission coefficients remain
valid at a fixed angle of incidence. Possibilities to exploit the new
relationships are discussed.Comment: submitted for publicatio
Near-Infrared Super Resolution Imaging with Metallic Nanoshell Particle Chain Array
We propose a near-infrared super resolution imaging system without a lens or
a mirror but with an array of metallic nanoshell particle chain. The imaging
array can plasmonically transfer the near-field components of dipole sources in
the incoherent and coherent manners and the super resolution images can be
reconstructed in the output plane. By tunning the parameters of the metallic
nanoshell particle, the plasmon resonance band of the isolate nanoshell
particle red-shifts to the near-infrared region. The near-infrared super
resolution images are obtained subsequently. We calculate the field intensity
distribution at the different planes of imaging process using the finite
element method and find that the array has super resolution imaging capability
at near-infrared wavelengths. We also show that the image formation highly
depends on the coherence of the dipole sources and the image-array distance.Comment: 15 pages, 6 figure
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